Create lockdown test for tag cloud

The tag cloud appears to have 100% code coverage, but it turns out that
there are no assertions regarding this part of the code, it just runs
without raising any exceptions.

Run the lockdown test with `bundle exec rake test:lockdown`.

The lockdown test is an `approval` test, meaning that whatever you
previously approved is considered the correct result.

The first time you run the test there is no previously approved result,
so the test will fail.

To make it pass copy the `.lockdown/received.html` file to
`.lockdown/approved.html`. By doing this you _approve_ the current
output as being correct.

If you run `bundle exec rake test:lockdown` again, the test should pass.
Create a tag cloud class

This duplicates the code in the controller.

We are calling the new class from the controller, but we are not yet
using the results. This ensures that the code can run without raising
any exceptions.
refactored get_stats_tags
renamed variables
refactored second sql query
major sql refactoring
major refactor of 90days stuff in TagCloud model
boom - massive refactoring to get_stats_tags method
refactored tags view
more refactoring of TagCloud class
complete refactoring and deletion of compute method
refactored the views
fixed merge conflicts